Ok, now follow this procedure:
grep password .my.cnf
Copy this password and then launch this commands:
service mysqld stop
mysqld_safe --skip-grant-tables &
mysql
FLUSH PRIVILEGES;
set password for 'root'@'localhost' = PASSWORD('yourcopiedpwd');
And then:
systemctl stop mysqld
systemctl start mysqld
If from service interface mysql remains stopped launch this other commands:
mysqladmin shutdown
systemctl start mysqld
Then I suggest you to create an admin account with all privileges with this mysql command:
GRANT ALL PRIVILEGES ON *.* TO 'admin'@'localhost' IDENTIFIED BY 'adminpassword';
You can use it for application like phpmyadmin.
Try to reboot the server and check if it works properly by log into mysql with mysql command. Process starts automatically only if you did systemctl enable mysqld before.
Then you can check if backup works properly with command
backup-data -b backup-data
Wait for your feedback.
Regards.